C. Guevara, J. Stutzki, V. Ossenkopf-Okada, U. Graf, Y. Okada, N. Schneider, P. F. Goldsmith, J. P. Pérez-Beaupuits, S. Kabanovic, M. Mertens, N. Rothbart, R. Güsten
{"title":"The [O I] fine structure line profiles in Mon R2 and M17 SW: The puzzling nature of cold foreground material identified by [12C II] self-absorption","authors":"C. Guevara, J. Stutzki, V. Ossenkopf-Okada, U. Graf, Y. Okada, N. Schneider, P. F. Goldsmith, J. P. Pérez-Beaupuits, S. Kabanovic, M. Mertens, N. Rothbart, R. Güsten","doi":"10.1051/0004-6361/202450530","DOIUrl":null,"url":null,"abstract":"<i>Context.<i/> Recent studies of the optical depth comparing [<sup>12<sup/>C II] and [<sup>13<sup/>C II] line profiles in Galactic star-forming regions have revealed strong self-absorption in [<sup>12<sup/>C II] by low excitation foreground material. This implies a high column density for C<sup>+<sup/>, corresponding to equivalent <i>A<i/><sub>V<sub/> values of a few (up to about 10) mag.<i>Aims.<i/> As the nature and origin of such a great column of cold C<sup>+<sup/> foreground gas are difficult to determine, it is essential to constrain the physical conditions of this material.<i>Methods.<i/> We conducted high-resolution observations of [O I] 63 μm and [O I] 145 μm lines in M17 SW and Mon R2. The [O I] 145 μm transition traces warm PDR-material, while the [O I] 63 μm line traces the foreground material, as manifested by the absorption dips.<i>Results.<i/> A comparison of both [O I] line profiles with [C II] isotopic lines confirm warm PDR-origin background emission and a significant column of cold foreground material, causing the self-absorption to be visible in the [<sup>12<sup/>C II] and [O I] 63 μm profiles. In M17 SW, the C<sup>+<sup/> and O<sup>0<sup/> column densities are comparable for both layers. Mon R2 exhibits larger O<sup>0<sup/> columns compared to C<sup>+<sup/>, indicating additional material where the carbon is neutral or in molecular form. Small-scale spatial variations in the foreground absorption profiles and the large column density (~10<sup>18<sup/> cm<sup>−2<sup/>) of the foreground material suggest the emission is coming from high-density regions associated with the cloud complex – and not a uniform diffuse foreground cloud.<i>Conclusions.<i/> The analysis confirms that the previously detected intense [C II] foreground absorption is attributable to a large column of low-excitation dense atomic material, where carbon is ionized and oxygen is in a neutral atomic form.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":null,"pages":null},"PeriodicalIF":5.4000,"publicationDate":"2024-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Astronomy & Astrophysics","FirstCategoryId":"101","ListUrlMain":"https://doi.org/10.1051/0004-6361/202450530","RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"ASTRONOMY & ASTROPHYSICS","Score":null,"Total":0}
引用次数: 0
Abstract
Context. Recent studies of the optical depth comparing [12C II] and [13C II] line profiles in Galactic star-forming regions have revealed strong self-absorption in [12C II] by low excitation foreground material. This implies a high column density for C+, corresponding to equivalent AV values of a few (up to about 10) mag.Aims. As the nature and origin of such a great column of cold C+ foreground gas are difficult to determine, it is essential to constrain the physical conditions of this material.Methods. We conducted high-resolution observations of [O I] 63 μm and [O I] 145 μm lines in M17 SW and Mon R2. The [O I] 145 μm transition traces warm PDR-material, while the [O I] 63 μm line traces the foreground material, as manifested by the absorption dips.Results. A comparison of both [O I] line profiles with [C II] isotopic lines confirm warm PDR-origin background emission and a significant column of cold foreground material, causing the self-absorption to be visible in the [12C II] and [O I] 63 μm profiles. In M17 SW, the C+ and O0 column densities are comparable for both layers. Mon R2 exhibits larger O0 columns compared to C+, indicating additional material where the carbon is neutral or in molecular form. Small-scale spatial variations in the foreground absorption profiles and the large column density (~1018 cm−2) of the foreground material suggest the emission is coming from high-density regions associated with the cloud complex – and not a uniform diffuse foreground cloud.Conclusions. The analysis confirms that the previously detected intense [C II] foreground absorption is attributable to a large column of low-excitation dense atomic material, where carbon is ionized and oxygen is in a neutral atomic form.
期刊介绍:
Astronomy & Astrophysics is an international Journal that publishes papers on all aspects of astronomy and astrophysics (theoretical, observational, and instrumental) independently of the techniques used to obtain the results.